Acetylenic oxazoles of proper design have been shown to undergo an intramolecular Diels-Alder reaction leading directly to fused-ring furan derivatives. With 5-alkoxyoxazoles the corresponding 2-alkoxyfurans are obtained, and these latter materials on acid hydrolysis rearrange to either methylene esters or methylbutenolides depending on the reaction conditions. The application of this concept to the synthesis of sesquiterpenes of biological interest is discussed.